endpoints

You should put the named parameters of the route regex into an optional capturing group: register_rest_route( ‘api’, ‘/animals(?:/(?P<id>\d+))?’, [ ‘methods’ => WP_REST_Server::READABLE, ‘callback’ => ‘get_animals’, ‘args’ => [ ‘id’ ], ] ); The second parameter is simply a regex, thus you can use normal regex logic to make it more complex